Systems and methods for control of superheat from a subcooler

ABSTRACT

Systems and methods for controlled subcooling of working fluid in a heating, ventilation, air conditioning and refrigeration (HVACR) system through a suction line heat exchanger are disclosed. The suction line heat exchanger may receive a first fluid flow travelling to a suction of the compressor in the HVACR system and second flow of working fluid that is travelling from a heat exchanger receiving the discharge of the compressor to an expansion device. Superheating of the first working fluid may be determined based on temperature measurements prior to and following the suction line heat exchanger. The superheating may be used to control the quantity of the second flow of working fluid introduced into the suction line heat exchanger, for example to maintain superheat that is below a threshold value. These systems may include chillers and heat pump systems, and methods may be applied to chillers or heat pump systems.

FIELD

This disclosure is directed to systems and methods for the control ofsuperheat generated by a subcooler in a heating, ventilation, airconditioning, and refrigeration (HVACR) system.

BACKGROUND

Subcooling can increase the difference in enthalpy between the condenserand the evaporator in a heating, ventilation, air conditioning, andrefrigeration (HVACR) system. This can improve the capacity andefficiency of an HVACR system over the capacity and efficiency of anHVACR system having identical values for the suction and dischargepressure of a compressor included in that HVACR system.

SUMMARY

This disclosure is directed to systems and methods for the control ofsuperheat generated by a subcooler in a heating, ventilation, airconditioning, and refrigeration (HVACR) system.

Subcooling can be provided to an HVACR system using a suction line heatexchanger, where working fluid can release additional heat prior toentering an expansion device, and the heat can be absorbed by workingfluid that is about to enter a suction of a compressor of the HVACRsystem. This subcooling can provide efficiency advantages.

Excessive subcooling may have detrimental effects on HVACR systemperformance. Depending on the operating mode of the HVACR system,excessive subcooling can result in issues including liquid slugging, orpotentially freezing at one of the heat exchangers of the HVACR system,and thus may require defrost cycles which cost efficiency.

Providing controlled subcooling through a suction line heat exchangermay allow the advantages of subcooling with respect to capacity andefficiency to be realized while avoiding some of the associated risks orproblems resulting from excessive subcooling. Control may be achieved byusing a flow director to control a portion of the flow through a suctionline heat exchanger, based on the superheat added to the suction lineworking fluid by the subcooled refrigerant. In some embodiments, theimprovements to efficiency can be improvements to overall efficiency ofheat pump operations, such as increase of heating capacity and reductionin power when at maximum heating capacity. In an embodiment, thecontrolled subcooling can provide an overall efficiency of heat pumpoperations of approximately 8%, for example by increasing the heatingcapacity by approximately 4% while also reducing energy consumption atmaximum heating capacity by approximately 4%.

An HVACR circuit embodiment includes a compressor having a suction and adischarge, a first heat exchanger, an expander, a second heat exchanger,and a suction line heat exchanger. The suction line heat exchanger isconfigured to exchange heat between a first working fluid flow, wherethe first working fluid flow is a flow of working fluid from one of thefirst heat exchanger and the second heat exchanger to the suction of thecompressor, and a second working fluid flow, where the second workingfluid flow is a flow of working fluid from the other of the first heatexchanger and the second heat exchanger towards the expander. The HVACRcircuit further includes a flow director configured to regulate anamount of the second working fluid flow entering the suction line heatexchanger. The HVACR circuit also includes a controller, configured toreceive a first temperature of the first working fluid flow prior toentering the suction line heat exchanger, receive a second temperatureof the first working fluid flow between the suction line heat exchangerand the suction of the compressor, determine a superheat generation atthe suction line heat exchanger based on the first temperature and thesecond temperature; and control the flow director based on the superheatgeneration and a threshold superheat value.

In an embodiment, the HVACR circuit further includes a third temperaturesensor configured to measure a temperature of the second working fluidflow prior to entering the flow director or at an inlet of the flowdirector, and the controller is configured to further control the flowdirector based on a reading from the third temperature sensor.

In an embodiment, in the HVACR circuit, the first heat exchanger is anoutdoor heat exchanger receiving working fluid from the discharge of thecompressor, the second heat exchanger is an evaporator, the firstworking fluid flow is from the second heat exchanger to the suction ofthe compressor, and the second working fluid flow is from the first heatexchanger to the expander.

In an embodiment, the HVACR circuit further includes a flow reverserconfigured to direct a discharge of the compressor to one of the firstheat exchanger and the second heat exchanger. In an embodiment, theHVACR circuit is in a cooling mode when the flow reverser directs adischarge of the compressor to the first heat exchanger, and a heatingmode when the flow reverser directs the discharge of the compressor tothe second heat exchanger. In an embodiment, when the HVACR circuit isin the cooling mode, the first working fluid flow is from the secondheat exchanger to the suction of the compressor, and the second workingfluid flow is from the first heat exchanger to the expander. In anembodiment, when the HVACR circuit is in the heating mode, the firstworking fluid flow is from the first heat exchanger to the suction ofthe compressor, and the second working fluid flow is from the secondheat exchanger to the expander.

In an embodiment, the suction line heat exchanger is a counter-flow heatexchanger.

In an embodiment, the flow director includes a stepped three-way valveand a bypass line.

In an embodiment, the flow director includes a plurality of controllablevalves, and wherein the controller is configured to operate theplurality of controllable valves proportionally.

In an embodiment, controlling the flow director based on the superheatgeneration and a threshold superheat value comprises regulating thesecond working fluid flow such that the superheat generation is lessthan the threshold superheat value. In an embodiment, the thresholdsuperheat value is at or about 4° C.

In an embodiment, the HVACR circuit includes a first temperature sensorlocated upstream of the suction line heat exchanger with respect to thefirst working fluid flow, and wherein the controller receives the firsttemperature from the first temperature sensor.

In an embodiment, the HVACR circuit includes a second temperature sensorlocated between the suction line heat exchanger and the suction of thecompressor, and wherein the controller receives the second temperaturefrom the second temperature sensor.

In an embodiment, a method of operating an HVACR circuit includesproviding a first working fluid flow through a suction line heatexchanger, wherein the first working fluid flow is a working fluid flowfrom a first heat exchanger to a suction of a compressor and providing asecond working fluid flow through the suction line heat exchanger,separate from the first working fluid flow. The second working fluidflow is a working fluid flow from a second heat exchanger to anexpander, and the first working fluid flow and the second working fluidflow exchange heat in the suction line heat exchanger. The methodincludes receiving a first temperature of the first working fluid flowat a position directly upstream of the suction line heat exchanger andreceiving a second temperature of the first working fluid flow at aposition directly downstream of the suction line heat exchanger. Themethod further includes determining a superheat generation based on thefirst temperature and the second temperature. The method also includescontrolling a quantity of flow of the second working fluid flow throughthe suction line heat exchanger based on the superheat generation and athreshold superheat value.

In an embodiment, the quantity of flow of the second working fluid flowis controlled such that the superheat generation does not exceed thethreshold superheat value. In an embodiment, the threshold superheatvalue is at or about 4° C.

In an embodiment, controlling the quantity of flow of the second workingfluid flow includes directing a portion of the second working fluid flowto a bypass line via a stepped three-way valve.

In an embodiment, controlling the quantity of flow of the second workingfluid flow includes operating a plurality of controllable valvesproportionally to allocate flow between a bypass line and the suctionline heat exchanger.

In an embodiment, the method further includes receiving a thirdtemperature, wherein the third temperature is a temperature of thesecond working fluid flow, and controlling the quantity of flow of thesecond working fluid flow is further based on the third temperature.

In an embodiment, the suction line heat exchanger is a counter-flow heatexchanger wherein the first working fluid flow travels through thesuction line heat exchanger in a first direction, and the second workingfluid flow travels through the suction line heat exchanger in a seconddirection, wherein the second direction is opposite the first direction.

In an embodiment, the HVACR circuit is a heat pump circuit, the firstheat exchanger is a heat exchanger receiving working fluid from theexpander, and the second heat exchanger is a heat exchanger receivingworking fluid from a discharge of the compressor.

DRAWINGS

FIG. 1 is a schematic of a heating, ventilation, air conditioning, andrefrigeration (HVACR) circuit according to an embodiment.

FIG. 2A is a schematic of an HVACR circuit according to an embodiment,wherein the HVACR circuit includes a heat pump in a cooling mode.

FIG. 2B is a schematic of an HVACR circuit according to an embodiment,wherein the HVACR circuit includes a heat pump in a heating mode.

FIG. 3A is a crosswise sectional view of a suction line heat exchangeraccording to an embodiment.

FIG. 3B is a schematic view of the suction line heat exchanger of FIG.3A according to an embodiment.

FIG. 4 is a flowchart of a method according to an embodiment.

DETAILED DESCRIPTION

This disclosure is directed to systems and methods for the control ofsuperheat generated by a subcooler in a heating, ventilation, airconditioning, and refrigeration (HVACR) system.

FIG. 1 is a schematic of a heating, ventilation, air conditioning, andrefrigeration (HVACR) circuit 100 according to an embodiment. HVACRcircuit 100 includes compressor 102, first heat exchanger 104, expansiondevice 106, second heat exchanger 108, and suction line heat exchanger110. HVACR circuit further includes fluid line 112, flow director 114,bypass line 116, and return line 118. HVACR circuit 100 also includesfirst temperature sensor 120 and second temperature sensor 122. HVACRcircuit 100 further includes controller 124. HVACR circuit 100 mayoptionally include a third temperature sensor 126.

Compressor 102 is a compressor that compresses a working fluid of theHVACR circuit 100. Compressor 102 may be any suitable type of compressorfor an HVACR system such as, for example, a screw compressor or a scrollcompressor. Compressor 102 includes suction 128, where the working fluidenters the compressor 102, and discharge 130, where compressed workingfluid exits the compressor 102.

First heat exchanger 104 receives the compressed working fluid exitingfrom discharge 130 of compressor 102. First heat exchanger 104 may be acondenser configured to allow the working fluid to release heat, forexample to another fluid, condensing the working fluid. In an embodimentwhere HVACR circuit 100 is part of an air-cooled chiller, first heatexchanger 104 may be an outdoor condenser configured to exchange heatbetween the working fluid and ambient outdoor air to condense thecompressed working fluid. In an embodiment, working fluid exits firstheat exchanger 104 via fluid line 112.

Expansion device 106 is a device configured to reduce the pressure ofthe working fluid. Expansion device 106 is an expander. As a result ofreduction in the pressure in the working fluid at expansion device 106,a portion of the working fluid is converted to a gaseous form. Expansiondevice 106 may be, for example, an expansion valve, orifice, or othersuitable expander to reduce pressure of a working fluid such as theworking fluid. In an embodiment, expansion device 106 includes multipleorifices. In an embodiment, the multiple orifices of expansion device106 have different sizes. Expansion device 106 may be a controllableexpansion device having a variable aperture. In an embodiment, expansiondevice 106 is an electronic expansion valve.

Second heat exchanger 108 is a heat exchanger receiving working fluidfrom expansion device 106. In an embodiment where HVACR circuit 100 ispart of a chiller, second heat exchanger may be an evaporator configuredto exchange heat between the working fluid and a process fluid such aswater or air to provide cooling to a building having climate controlprovided by a system including the HVACR circuit 100. In thisembodiment, the working fluid in second heat exchanger 108 may absorbheat from the process fluid to evaporate the working fluid. The workingfluid exiting second heat exchanger 108 may pass to suction line heatexchanger 110.

Suction line heat exchanger 110 is a heat exchanger allowing theexchange of heat between two working fluid flows through HVACR circuit100. Suction line heat exchanger 110 may receive a first flow of workingfluid from second heat exchanger 108, which then passes to suction 128of compressor 102 following the exchange of heat within suction lineheat exchanger 110. Suction line heat exchanger 110 may receive a secondflow of working fluid from flow director 114, which then passes toreturn line 118 following the exchange of heat within suction line heatexchanger 110. Suction line heat exchanger 110 may be any suitable formof heat exchanger for exchanging heat between the first and second flowsof working fluid. In an embodiment, suction line heat exchanger 110 isconstructed of one or more steel materials. In an embodiment, suctionline heat exchanger 110 does not include copper. In an embodiment,suction line heat exchanger 110 includes a plurality of tubes conveyingthe first flow of working fluid, located within an outer pipe throughwhich the second flow of working fluid travels. In an embodiment,suction line heat exchanger 110 is a counter-flow heat exchanger wherethe first flow of working fluid and the second flow of working fluidtravel in opposite directions.

Fluid line 112 may direct the fluid exiting heat exchanger 104 to flowdirector 114. Flow director 114 allocates the flow from fluid line 112among the suction line heat exchanger 110 and a bypass line 116. Flowdirector 114 may be any one or more flow controls that are configured toallow a variable amount of the flow exiting heat exchanger 104 to bedirected to the suction line heat exchanger 110. Flow director 114 mayregulate the flow entering suction line heat exchanger 110 based oncontrol by controller 124. Bypass line 116 is a fluid line that conveysfluid from flow director 114 to return line 118 without passing throughsuction line heat exchanger 110. Return line 118 is a line that conveysfluid received from suction line heat exchanger 110 and bypass line 116to the expansion device 106.

Flow director 114 may be, for example, a three-way valve. In anembodiment, flow director 114 is a motorized, stepped three-way valve.In an embodiment where flow director 114 is a three-way valve, thethree-way valve has one input receiving flow from fluid line 112, afirst outlet from which fluid passes to suction line heat exchanger 110,and a second outlet from which fluid passes to bypass line 116.

In an embodiment, flow director 114 includes at least twovariable-position valves. In this embodiment, the at least twovariable-position valves may be controlled in a complementary fashion,where the extent of opening of each valve is controlled with respect tothe others to allocate the flow among suction line heat exchanger 110and bypass line 116. This complementary control may be proportional, forexample, having the aperture of the variable-position valve controllingflow to suction line heat exchanger 110 be set to a size proportional tothe amount of flow to be directed to the suction line heat exchanger 110while also having the variable-position valve controlling flow to bypassline 116 be set to a size proportional to the amount of flow to bedirected to the bypass line 116. Proportional control of valves in flowdirector 114 may be directed by controller 124.

In an embodiment, flow director 114 includes multiple valves of varyingaperture size for each of suction line heat exchanger 110 and bypassline 116 and the allocation of flow is achieved by opening or closingone or more of those multiple valves.

In an embodiment, first temperature sensor 120 is a temperature sensorlocated directly upstream of or at an inlet of the suction line heatexchanger 110 with respect to the flow of working fluid through theHVACR circuit 100. First temperature sensor 120 is a sensor configuredto obtain a temperature value, either directly or indirectly. Firsttemperature sensor 120 may obtain a first temperature reading that is atemperature of the first working fluid flow prior to the first workingfluid flow exchanging heat in the suction line heat exchanger 110. Thefirst temperature sensor 120 may be any suitable temperature sensor formeasuring a temperature of a working fluid flow prior to that workingfluid flow entering the suction line heat exchanger 110. Firsttemperature sensor 120 may be operatively coupled to controller 124 suchthat it can provide a first temperature reading to controller 124. Theoperative coupling may be through any suitable connection to provide thefirst temperature reading, such as wired or wireless communications.

In an embodiment, second temperature sensor 122 is a temperature sensorlocated directly downstream of or at an outlet of the suction line heatexchanger 110 with respect to the flow of working fluid through theHVACR circuit 100. Second temperature sensor 122 is a sensor configuredto obtain a temperature value, either directly or indirectly. Secondtemperature sensor 122 may obtain a second temperature reading that isthe temperature of the first working fluid flow subsequent to thatworking fluid flow exchanging heat at suction line heat exchanger 110.Second temperature sensor 122 is upstream of the compressor 102. Secondtemperature sensor 122 may be operatively coupled to controller 124 suchthat it can provide the second temperature reading to controller 124.The operative coupling may be through any suitable connection to providethe second temperature reading, such as wired or wirelesscommunications.

Controller 124 includes a processor. Controller 124 is operativelycoupled to first temperature sensor 120 and second temperature sensor122. Controller 124 is further operatively coupled to flow director 114such that the quantity of flow to suction line heat exchanger 110 can becontrolled. Controller 124 may be configured to receive a firsttemperature from the first temperature sensor. Controller 124 may beconfigured to receive a second temperature from the second temperaturesensor. Controller 124 may be configured to determine a superheatgeneration at the suction line heat exchanger based on the firsttemperature and the second temperature. In an embodiment, the superheatgeneration is determined by subtracting the first temperature from thesecond temperature. Controller 124 may further be configured to controlthe flow director 114 based on the superheat generation and a thresholdsuperheat value. Controller 124 may include a memory, and the memory maybe configured to store at least the threshold superheat value. Thethreshold superheat value may be a value of superheat that ispermissible for HVACR circuit 100 during operations. The thresholdsuperheat value may be based on parameters such as, for example, thedesign of the HVACR circuit 100, and optionally the amount of workingfluid that HVACR circuit 100 has been charged with. In an embodiment,the threshold superheat value is determined based on a superheatsetpoint of the HVACR circuit 100. In an embodiment, the thresholdsuperheat value may be at or about 4° C. The threshold superheat valuemay be a value selected based on one or more of, for example, avoidingliquid slugging or improving stability at the expansion device 106. Thethreshold superheat value may further be dynamic with the variation inthe threshold superheat value being based at least in part on, forexample, ambient air temperature, saturated suction temperature, and/orcompressor load of compressor 102.

Optionally, third temperature sensor 126 may be included in HVACRcircuit 100. Third temperature sensor 126 may be located along fluidline 112. Third temperature sensor 126 may be any suitable temperaturesensor for measuring a temperature of the working fluid within fluidline 112. Third temperature sensor 126, when included, may measure athird temperature reading that is a temperature of the second workingfluid flow that introduced into suction line heat exchanger 110. Thirdtemperature sensor 126, when included, may be operatively coupled tocontroller 124 such that it can provide the third temperature reading tocontroller 124. The operative coupling may be through any suitableconnection to provide the second temperature reading, such as wired orwireless communications. In an embodiment where third temperature sensor126 is included, the controller 124 may be further configured todetermine the amount of flow for flow director 114 to allow into suctionline heat exchanger 110 based on the third temperature reading.

FIG. 2A is a schematic of an HVACR circuit 200 according to anembodiment, wherein the HVACR circuit includes a heat pump in a coolingmode. HVACR circuit 200 includes compressor 202, flow reverser 204,first heat exchanger 206 and second heat exchanger 208. HVACR circuit200 optionally includes drier 210. HVACR circuit 200 includes fluid line212 which conveys fluid to flow director 214. Flow director 214allocates flow among bypass line 216 and suction line heat exchanger218. Suction line heat exchanger 218 and bypass line 216 convey fluid toreturn line 220. HVACR circuit 200 further includes expansion device222. HVACR circuit 200 further includes first temperature sensor 224 andsecond temperature sensor 226. HVACR circuit 200 also includescontroller 228. Optionally, third temperature sensor 234 may also beincluded in HVACR circuit 200.

In the cooling mode shown in FIG. 2A, flow reverser 204 directs thedischarge of compressor 202 to first heat exchanger 206. In the coolingmode shown in FIG. 2A, check valves 236 permit the flow of the workingfluid from the first heat exchanger 206 to optional drier 210 or fluidline 212.

Compressor 202 includes suction 230 and discharge 232. Compressor 202 isa compressor that compresses a working fluid of the HVACR circuit 200.Compressor 202 may be, for example, any suitable type of compressor foran HVACR system, such as a screw compressor. Compressor 202 includessuction 230, where the working fluid enters the compressor 202, anddischarge 232, where compressed working fluid exits the compressor 202.

Flow reverser 204 is a flow control configured to allow the direction offlow through HVACR circuit 200 to be switched between a first directionand a second direction, opposite the first. In an embodiment, flowreverser 204 is a four-way valve. In an embodiment where flow reverser204 is a four-way valve, the four-way valve may have a first connectionto the discharge 232 of compressor 202, a second connection to firstheat exchanger 206, a third connection to the second heat exchanger 208,and a fourth connection to the suction line heat exchanger 218. In thisembodiment, when HVACR circuit 200 is in a cooling mode, the firstconnection to discharge 232 is connected to the third connection tosecond heat exchanger 208, and the second connection to first heatexchanger 206 is connected to the fourth connection to the suction lineheat exchanger 218.

First heat exchanger 206 is a heat exchanger allowing the working fluidto exchange heat as part of a heating or cooling operation of HVACRcircuit 200. In an embodiment, first heat exchanger 206 is an outdoorheat exchanger. In an embodiment, in the cooling mode, first heatexchanger 206 receives working fluid compressed by the compressor 202from flow reverser 204. In this embodiment, in the cooling mode, firstheat exchanger 206 operates as a condenser allowing the compressedworking fluid to reject heat to an ambient environment. In thisembodiment, in the cooling mode, the working fluid leaving the firstheat exchanger 206 then travels to one of optional drier 210 and flowdirector 214 via fluid line 212.

Second heat exchanger 208 is another heat exchanger separate from firstheat exchanger 206. In an embodiment, second heat exchanger 208 createsa heat exchange relationship between the working fluid and a processfluid such as water or air. In an embodiment, in the cooling mode, thesecond heat exchanger 208 receives working fluid from expansion device222. In this embodiment, in the cooling mode, the second heat exchangerfunctions as an evaporator where the working fluid absorbs heat from theprocess fluid to provide cooling to a space serviced by an HVACR systemincluding HVACR circuit 200. In this embodiment, in the cooling mode,the working fluid exiting the second heat exchanger 208 passes to flowreverser 204.

HVACR circuit 200 may optionally include drier 210. Drier 210 mayreceive working fluid from the first heat exchanger 206 when HVACRcircuit 200 is in the cooling mode as shown in FIG. 2A.

Fluid line 212 conveys the working fluid in HVACR circuit 200 to flowdirector 214. In an embodiment including optional drier 210, the fluidline 212 may be from drier 210 to flow director 214. In an embodiment,fluid line 212 may receive working fluid from the first heat exchanger206 when the HVACR circuit 200 is in the cooling mode as shown in FIG.2A

Flow director 214 receives working fluid from fluid line 212. Flowdirector 214 allocates the received working fluid among bypass line 216and suction line heat exchanger 218. By controlling the amount ofworking fluid allocated to suction line heat exchanger 218, thesuperheat and subcooling occurring at suction line heat exchanger 218can be controlled. The allocation of working fluid among bypass line 216and suction line heat exchanger 218 may be determined by controller 228,which may direct flow director 214 to allocate the flow according to acommand.

Flow director 214 may be, for example, a three-way valve. In anembodiment, flow director 214 is a motorized, stepped three-way valve.In an embodiment where flow director 214 is a three-way valve, thethree-way valve has one input receiving flow from fluid line 212, afirst outlet from which fluid passes to suction line heat exchanger 218,and a second outlet from which fluid passes to bypass line 216.

In an embodiment, flow director 214 includes at least twovariable-position valves. In this embodiment, the at least twovariable-position valves may be controlled in a complementary fashion,where the extent of opening of each valve is controlled with respect tothe others to allocate the flow among suction line heat exchanger 218and bypass line 216. This complementary control may be proportional, forexample, having the aperture of the variable-position valve controllingflow to suction line heat exchanger 218 be set to a size proportional tothe amount of flow to be directed to the suction line heat exchanger 218while also having the variable-position valve controlling flow to bypassline 216 be set to a size proportional to the amount of flow to bedirected to the bypass line 216. Proportional control of valves in flowdirector 214 may be directed by controller 228.

In an embodiment, flow director 214 includes multiple valves of varyingaperture size for each of suction line heat exchanger 218 and bypassline 216 and the allocation of flow is achieved by opening or closingone or more of those multiple valves.

Bypass line 216 allows fluid from flow director 214 to pass to returnline 220 without passing through suction line heat exchanger 218. Bypassline 216 may receive working fluid from flow director 214, depending onthe amount of fluid directed to suction line heat exchanger 218.

Suction line heat exchanger 218 allows a first flow of working fluidfrom flow reverser 204 to suction 230 of compressor 202 to exchange heatwith a second flow of working fluid from flow director 214. In anembodiment, the first flow of working fluid is a suction gas. In anembodiment, the second flow of working fluid is a liquid at a relativelyhigher temperature than the first flow of working fluid. In anembodiment, heat exchange at suction line heat exchanger superheats thefirst flow of working fluid and subcools the second flow of workingfluid. In an embodiment, a quantity of fluid included in the second flowof working fluid affects the extent of superheating and/or subcoolingoccurring as a result of the heat exchange at suction line heatexchanger 218. In an embodiment, the first flow of working fluid travelsthrough a plurality of tubes and the second flow of working fluidtravels through an outer pipe surrounding the plurality of tubes. In anembodiment, the suction line heat exchanger 218 includes a steelmaterial. In an embodiment, suction line heat exchanger 218 does notinclude copper. In an embodiment, suction line heat exchanger is acounter flow heat exchanger where the first working fluid flow and thesecond working fluid flow travel in opposite directions through suctionline heat exchanger 218.

Return line 220 receives the working fluid from the bypass line 216 andthe second working fluid flow exiting the suction line heat exchanger218, and conveys the received working fluid to expansion device 222.

Expansion device 222 is a device configured to reduce the pressure ofthe working fluid. As a result, a portion of the working fluid isconverted to a gaseous form. Expansion device 222 may be, for example,an expansion valve, orifice, or other suitable expander to reducepressure of a working fluid such as the working fluid. In an embodiment,expansion device 222 includes multiple orifices. In an embodiment, themultiple orifices of expansion device 222 have different sizes.Expansion device 222 may be a controllable expansion device having avariable aperture. In an embodiment, expansion device 222 is anelectronic expansion valve.

First temperature sensor 224 is a temperature sensor located directlyupstream of or at an inlet of the suction line heat exchanger 218 withrespect to the flow of working fluid through the HVACR circuit 200.First temperature sensor 224 may be located between the fourthconnection of the flow reverser 204 and the suction line heat exchanger218. First temperature sensor 224 may obtain a first temperature readingthat is a temperature of the first working fluid flow prior to the firstworking fluid flow exchanging heat in the suction line heat exchanger218. The first temperature sensor 224 may be any suitable temperaturesensor for measuring a temperature of a working fluid flow prior to thatworking fluid flow entering the suction line heat exchanger 218. Firsttemperature sensor 224 may be operatively coupled to controller 228 suchthat it can provide a first temperature reading to controller 228. Theoperative coupling may be through any suitable connection to provide thefirst temperature reading, such as wired or wireless communications.

Second temperature sensor 226 is a temperature sensor located directlydownstream of or at an outlet of the suction line heat exchanger 218with respect to the flow of working fluid through the HVACR circuit 200.Second temperature sensor 226 may obtain a second temperature readingthat is the temperature of the first working fluid flow subsequent tothat working fluid flow exchanging heat at suction line heat exchanger218. Second temperature sensor 226 is upstream of the compressor 202.Second temperature sensor 226 may be operatively coupled to controller228 such that it can provide the second temperature reading tocontroller 228. The operative coupling may be through any suitableconnection to provide the second temperature reading, such as wired orwireless communications.

Controller 228 includes a processor. Controller 228 is operativelycoupled to first temperature sensor 224 and second temperature sensor226. Controller 228 is further operatively coupled to flow director 214such that the quantity of flow to suction line heat exchanger 218 can becontrolled. Controller 228 may be configured to receive a firsttemperature from the first temperature sensor. Controller 228 may beconfigured to receive a second temperature from the second temperaturesensor. Controller 228 may be configured to determine a superheatgeneration at the suction line heat exchanger based on the firsttemperature and the second temperature. In an embodiment, the superheatgeneration is determined by subtracting the first temperature from thesecond temperature. Controller 228 may further be configured to controlthe flow director 214 based on the superheat generation and a thresholdsuperheat value. Controller 228 may include a memory, and the memory maybe configured to store at least the threshold superheat value. Thethreshold superheat value may be a value of superheat that ispermissible for HVACR circuit 200 during operations. The thresholdsuperheat value may be based on parameters such as, for example, thedesign of the HVACR circuit 200, and optionally the amount of workingfluid that HVACR circuit 200 has been charged with. In an embodiment,the threshold superheat value is determined based on a superheatsetpoint of the HVACR circuit 100. In an embodiment, the thresholdsuperheat value may be at or about 4° C. The threshold superheat valuemay be a value selected based on one or more of, for example, avoidingliquid slugging or improving stability at the expansion device 222. Thethreshold superheat value may further be dynamic with the variation inthe threshold superheat value being based at least in part on, forexample, ambient air temperature, saturated suction temperature, and/orcompressor load of compressor 202.

Optionally, third temperature sensor 234 may be included in HVACRcircuit 200. Third temperature sensor 234 may be located between flowdirector 214 and suction line heat exchanger 218. Third temperaturesensor 234 may be any suitable temperature sensor for measuring atemperature of the working fluid between flow director 214 and suctionline heat exchanger 218. Third temperature sensor 234, when included,may measure a third temperature reading that is a temperature of thesecond working fluid flow that introduced into suction line heatexchanger 218. Third temperature sensor 234, when included, may beoperatively coupled to controller 228 such that it can provide the thirdtemperature reading to controller 228. The operative coupling may bethrough any suitable connection to provide the third temperaturereading, such as wired or wireless communications. In an embodimentwhere third temperature sensor 234 is included, the controller 228 maybe further configured to determine the amount of flow for flow director214 to allow into suction line heat exchanger 218 based on the thirdtemperature reading.

FIG. 2B is a schematic of an HVACR circuit 200 according to anembodiment, wherein the HVACR circuit includes a heat pump in a heatingmode. The HVACR circuit 200 includes the components discussed above inFIG. 2A. In the heating mode shown in FIG. 2B, flow reverser 204 directsthe discharge of compressor 202 to second heat exchanger 208. In theheating mode shown in FIG. 2B, check valves 236 permit the flow of theworking fluid from the second heat exchanger 208 to optional drier 210or fluid line 212.

When HVACR circuit 200 is in a heating mode as shown in FIG. 2B, thefirst connection to discharge 232 is connected to the second connectionto first heat exchanger 206 and the third connection to second heatexchanger 208 is connected to the fourth connection to the suction lineheat exchanger 218.

When HVACR circuit 200 is in a heating mode as shown in FIG. 2B, secondheat exchanger 208 receives process fluid compressed by compressor 202via the flow reverser 204. In this embodiment, in the heating mode, thesecond heat exchanger 208 operates as a condenser allowing thecompressed working fluid to reject heat to the process fluid to provideheating to the space served by the HVACR system including HVACR circuit200. In this embodiment, in the heating mode, the working fluid leavingthe second heat exchanger then travels to one of optional drier 210 andflow director 214 via fluid line 212.

Drier 210 may receive working fluid from the heat exchanger 208 when theHVACR circuit 200 is in a heating mode as shown in FIG. 2B.

In an embodiment, fluid line 212 may receive working fluid from thesecond heat exchanger 208 when the HVACR circuit 200 is in a heatingmode as shown in FIG. 2B

When HVACR circuit 200 is in the heating mode as shown in FIG. 2B, firstheat exchanger 206 receives working fluid from expansion device 222. Inan embodiment, in the heating mode, first heat exchanger 206 functionsas an evaporator where the working fluid absorbs heat from the ambientenvironment. In this embodiment, in the heating mode, the working fluidexiting the first heat exchanger 206 passes to flow reverser 204.

FIG. 3A is a sectional view of a suction line heat exchanger 300according to an embodiment. Suction line heat exchanger 300 includesouter pipe 302 and a plurality of tubes 304. Outer pipe 302 conveys aflow of liquid working fluid, from a heat exchanger of the HVACR circuittowards an expansion device of that HVACR circuit. Tubes 304 conveyanother flow of gaseous working fluid, from another heat exchanger of anHVACR circuit towards a suction of a compressor of that HVACR circuit.The flow of liquid working fluid enters through inlet 306 and exitsthrough outlet 308. In an embodiment, the working fluid in tubes 304absorbs heat from the working fluid in outer pipe 302, superheating thesuction gas while subcooling the liquid working fluid. In an embodiment,the suction line heat exchanger 300 is a counter-flow heat exchanger,where a direction of the first flow of the working fluid in outer pipe302 is opposite a direction of the second flow of the working fluid intubes 304, such as the flow within outer pipe 302 being out of the page,whereas the flow of the working fluid in tubes 304 being into of thepage.

FIG. 3B is a schematic view of the suction line heat exchanger 300according to an embodiment. In FIG. 3B, outer tube 302 is not shown sothat tubes 304 and baffles 310 can be shown. Inlet 306 and outlet 308are shown. Inlet 306 allows the first flow of the working fluid to enterouter pipe 302. The flow of liquid working fluid is directed by baffles310 as it passes through outer pipe 302 to outlet 308. The flow ofgaseous working fluid passes from gas inlet 312 to gas outlet 314 viathe tubes 314. In an embodiment, the direction of the flow of gaseousworking fluid is opposite the direction of liquid working fluid, asshown in the arrangement of inlets and outlets shown in FIG. 3B.

FIG. 4 is a flowchart of a method 400 according to an embodiment. Method400 includes providing a first working fluid flow to a suction line heatexchanger 402 and providing a second working fluid flow to the suctionline heat exchanger 404. Method 400 further includes receiving a firsttemperature of the first working fluid flow directly upstream of thesuction line heat exchanger 406 and receiving a second temperature ofthe first working fluid flow directly downstream of the suction lineheat exchanger 408. Method 400 also includes determining a superheatgeneration 410 based on the first temperature and the secondtemperature, and controlling a quantity of flow of the second workingfluid flow to the suction line heat exchanger 412 based on the superheatgeneration and a threshold superheat value. Optionally, a thirdtemperature in the second working fluid flow can be received 414.

Method 400 includes providing a first working fluid flow to a suctionline heat exchanger 402. The first working fluid flow may be a flow of aworking fluid from a heat exchanger receiving the working fluid from anexpansion device towards a suction of a compressor of an HVACR circuitin which method 400 is being performed. In an embodiment, the firstworking fluid flow is of a gas at a relatively low temperature. In anembodiment, the first working fluid flow is of suction gas in the HVACRcircuit. In an embodiment where the HVACR circuit is incorporated into achiller, the first working fluid flow may be from an evaporator used toabsorb heat from a process fluid such as air or water. In an embodimentwhere the HVACR circuit is incorporated into a heat pump, the firstworking fluid flow may be from either an outdoor heat exchanger beingused as an evaporator to absorb heat from an ambient environment when ina heating mode, or a heat exchanger being used as an evaporator toabsorb heat from a process fluid such as air or water when the HVACRcircuit is in a cooling mode.

Method 400 also includes providing a second working fluid flow to thesuction line heat exchanger 404. The second working fluid flow may be aflow of working fluid from a heat exchanger that receives working fluidfrom the discharge of a compressor of the HVACR circuit towards anexpansion device of the HVACR circuit. In an embodiment, the secondworking fluid flow is from a liquid line in the HVACR circuit. In anembodiment, the second working fluid flow is a relatively warm liquidflow (i.e. at a temperature higher than that of the first working fluidflow provided at 402). In an embodiment where the HVACR circuit isincorporated into a chiller, the second working fluid flow may be from acondenser used to reject heat to an ambient environment and upstream ofan expansion device of the HVACR circuit. In an embodiment where theHVACR circuit is incorporated into a heat pump, the second working fluidflow may be from an indoor unit operating as a condenser to heat aprocess fluid such as air or water to provide heating in a heating mode,or a heat exchanger operating as a condenser to reject heat to anambient environment when in a heating mode.

In an embodiment, the first working fluid flow provided at 402 and thesecond working fluid flow provided at 404 are kept separate within thesuction line heat exchanger, exchanging heat with one another withoutany mixing occurring. In an embodiment, the suction line heat exchangeris a counter flow heat exchanger, where the first working fluid flowprovided at 402 and the second working fluid flow provided at 404respectively travel in directions opposite to one another in at least aportion of the suction line heat exchanger.

A first temperature of the first working fluid flow directly upstream ofthe suction line heat exchanger is received 406. The first temperaturemay be obtained from, for example, a temperature sensor located directlyupstream of the suction line heat exchanger. Directly upstream of thesuction line heat exchanger is understood as being where no othercomponent of the fluid circuit such as a heat exchanger, compressor,etc. are between the point of measurement and the suction line heatexchanger, aside from the fluid line conveying the working fluid to thesuction line heat exchanger. The first temperature received at 406 maybe measured at an inlet of the suction line heat exchanger. The firsttemperature received at 406 may be measured along a fluid line betweenthe outlet of the heat exchanger receiving working fluid from theexpansion device and the inlet of the suction line heat exchanger. Thefirst temperature may be communicated to a controller via an operationalcoupling such as a wired or wireless connection between a temperaturesensor taking the measurement and the controller.

A second temperature of the first working fluid flow directly downstreamof the suction line heat exchanger is received at 408. Directlydownstream of the suction line heat exchanger is understood as beinganywhere between the suction line heat exchanger and the next componentof the fluid circuit other than a fluid line following the suction lineheat exchanger, such as the suction of the compressor. The secondtemperature received at 408 may be obtained from, for example, atemperature sensor. The second temperature is a temperature of the firstworking fluid flow between the outlet of the suction line heat exchangerand a suction of the compressor of the HVACR circuit where method 400 isperformed. In an embodiment, the second temperature is received 408 atthe outlet of the suction line heat exchanger. In an embodiment, thesecond temperature is received 408 along a fluid line connecting thesuction line heat exchanger to the suction of the compressor. The secondtemperature may be communicated to a controller via an operationalcoupling such as a wired or wireless connection between a temperaturesensor taking the measurement and the controller.

A superheat generation is determined 410 based on the first temperatureand the second temperature. The superheat generation 410 is a measure ofthe superheat added to the suction gas by the suction line heatexchanger. In an embodiment, the superheat generation is determined asthe difference between the second temperature received at 408 and thefirst temperature received at 406. In an embodiment, the superheatgeneration may be determined 410 by a controller receiving the firsttemperature at 406 and the second temperature received at 408, forexample by an operative coupling such as a wired or wireless connectionbetween the controller and the sensors measuring the respective firstand second temperatures.

A quantity of flow of the second working fluid flow to the suction lineheat exchanger is controlled 412 based on the superheat generationdetermined at 410 and a threshold superheat value. The thresholdsuperheat value may be a value of superheat that is permissible forHVACR circuit during method 400. The threshold superheat value may bebased on parameters such as, for example, the design of the HVACRcircuit and optionally the amount of working fluid that HVACR circuithas been charged with. In an embodiment, the threshold superheat valueis determined based on a superheat setpoint of the HVACR circuit 100. Inan embodiment, the threshold superheat value may be at or about 4° C.The threshold superheat value may be a value selected based on one ormore of, for example, avoiding liquid slugging or improving stability atan expansion device. The threshold superheat value may further bedynamic with the variation in the threshold superheat value being basedat least in part on, for example, ambient air temperature, saturatedsuction temperature, and/or compressor load of a compressor of the HVACRsystem. In an embodiment, when the superheat generation determined at410 exceeds the threshold superheat value, the quantity of flow of thesecond working fluid flow may be reduced at 412. In an embodiment, whenthe superheat generation determined at 410 is less than the thresholdsuperheat value, the quantity of flow of the second working fluid flowmay be maintained or increased at 412. In an embodiment, the quantity offlow of the second working fluid flow and the superheat generation maybe used to determine a relationship between the quantity of flow of thesecond working fluid flow into the suction line heat exchanger and thesuperheat generation, and this relationship may be used to determine avalue for the quantity of flow of the second working fluid flow toprovide superheating at or near the threshold superheat value.

In an embodiment, control of the quantity of flow of the second workingfluid flow may be achieved through the controller directing a flowdirector to operate. The flow director controlled by the controller toeffect control of the quantity of flow of the second working fluid flowat 412 may be one or more flow controls that are configured to controlthe quantity of fluid allowed to flow into the suction line heatexchanger. The flow director may, for example, allocate the flow offluid between the suction line heat exchanger and a bypass line thatallows fluid to continue flow through the HVACR circuit without passingthrough the suction line heat exchanger. In an embodiment, the flowdirector is a three-way valve. In an embodiment, the flow director is amotorized, stepped three-way valve. In an embodiment, the flow directorhas one input, a first outlet from which fluid passes to suction lineheat exchanger, and a second outlet from which fluid passes to bypassline. In an embodiment, the flow director includes at least twovariable-position valves. In this embodiment, the at least twovariable-position valves may be controlled in a complementary fashion,where the extent of opening of each valve is controlled with respect tothe others to allocate the flow among the suction line heat exchangerand the bypass line. In an embodiment, the control of the at least twovariable-position valves is proportional control. In an embodiment, theflow director includes multiple valves of varying aperture size for eachof the suction line heat exchanger and bypass line and the allocation offlow is achieved by opening or closing one or more of those multiplevalves

Optionally, a third temperature in the second working fluid flow can bereceived 414. The temperature can be measured upstream of the flowdirector used to control the quantity of flow of the second workingfluid flow to the suction line heat exchanger at 412. The thirdtemperature may be used by the controller to further determine thequantity of flow of the second working fluid to be directed to thesuction line heat exchanger at 412. For example, the third temperaturecan be a parameter used to determine an expected superheating providedby a quantity of flow of the second working fluid flow into the suctionline heat exchanger at 412, and the expected superheating used toprovide superheating in an amount below the threshold superheat value.

In an embodiment, the method 400 may be continuous. In an embodiment,the method 400 may iterate by returning from the control of the quantityof the flow of the second working fluid flow at 412 to the measurementof the first temperature at 406, either continuously, at set intervals,or based on triggers such as changes in operating conditions.

Aspects:

It is understood that any of aspects 1-14 can be combined with any ofaspects 15-22.

-   -   Aspect 1. A heating, ventilation, air conditioning, and        refrigeration (HVACR) circuit, comprising:    -   a compressor having a suction and a discharge;    -   a first heat exchanger;    -   an expander;    -   a second heat exchanger;    -   a suction line heat exchanger, configured to exchange heat        between a first working fluid flow, wherein the first working        fluid flow is a flow of working fluid from one of the first heat        exchanger or the second heat exchanger to the suction of the        compressor, and a second working fluid flow, wherein the second        working fluid flow is a flow of working fluid from the other of        the first heat exchanger or the second heat exchanger towards        the expander;    -   a flow director configured to regulate an amount of the second        working fluid flow entering the suction line heat exchanger; and    -   a controller, configured to:        -   receive a first temperature of the first working fluid flow            prior to entering the suction line heat exchanger;        -   receive a second temperature of the first working fluid flow            between the suction line heat exchanger and the suction of            the compressor;        -   determine a superheat generation at the suction line heat            exchanger based on the first temperature and the second            temperature; and        -   control the flow director based on the superheat generation            and a threshold superheat value.    -   Aspect 2. The HVACR circuit according to aspect 1, wherein the        controller is further configured to receive a third temperature        of the second working fluid flow prior to entering the flow        director or at an inlet of the flow director further control the        flow director based on the third temperature.    -   Aspect 3. The HVACR circuit according to any of aspects 1-2,        wherein the first heat exchanger is an outdoor heat exchanger        receiving working fluid from the discharge of the compressor,        the second heat exchanger is an evaporator, the first working        fluid flow is from the second heat exchanger to the suction of        the compressor, and the second working fluid flow is from the        first heat exchanger to the expander.    -   Aspect 4. The HVACR circuit according to any of aspects 1-2,        further comprising a flow reverser configured to direct a        discharge of the compressor to one of the first heat exchanger        or the second heat exchanger.    -   Aspect 5. The HVACR circuit according to aspect 4, wherein the        HVACR circuit is in a cooling mode when the flow reverser        directs a discharge of the compressor to the first heat        exchanger, and a heating mode when the flow reverser directs the        discharge of the compressor to the second heat exchanger.    -   Aspect 6. The HVACR circuit according to aspect 5, wherein when        in the cooling mode, the first working fluid flow is from the        second heat exchanger to the suction of the compressor, and the        second working fluid flow is from the first heat exchanger to        the expander.    -   Aspect 7. The HVACR circuit according to any of aspects 5-6,        wherein when in the heating mode, the first working fluid flow        is from the first heat exchanger to the suction of the        compressor, and the second working fluid flow is from the second        heat exchanger to the expander.    -   Aspect 8. The HVACR circuit according to any of aspects 1-7,        wherein the suction line heat exchanger is a counter-flow heat        exchanger.    -   Aspect 9. The HVACR circuit according to any of aspects 1-8,        wherein the flow director comprises a stepped three-way valve        and a bypass line.    -   Aspect 10. The HVACR circuit according to any of aspects 1-8,        wherein the flow director comprises a plurality of controllable        valves, and wherein the controller is configured to operate the        plurality of controllable valves proportionally.    -   Aspect 11. The HVACR circuit according to any of claims 1-10,        wherein controlling the flow director based on the superheat        generation and a threshold superheat value comprises regulating        the second working fluid flow such that the superheat generation        is less than the threshold superheat value.    -   Aspect 12. The HVACR circuit according to aspect 11, wherein the        threshold superheat value is at or about 4° C.    -   Aspect 13 The HVACR circuit according to any of aspects 1-12,        further comprising a first temperature sensor located upstream        of the suction line heat exchanger with respect to the first        working fluid flow, and wherein the controller receives the        first temperature from the first temperature sensor.    -   Aspect 14. The HVACR circuit according to any of aspects 1-13,        further comprising a second temperature sensor located between        the suction line heat exchanger and the suction of the        compressor, and wherein the controller receives the second        temperature from the second temperature sensor.    -   Aspect 15. A method of operating a heating, ventilation, air        conditioning, and refrigeration (HVACR) circuit, comprising:    -   providing a first working fluid flow through a suction line heat        exchanger, wherein the first working fluid flow is a working        fluid flow from a first heat exchanger to a suction of a        compressor;    -   providing a second working fluid flow through the suction line        heat exchanger, separate from the first working fluid flow,        wherein the second working fluid flow is a working fluid flow        from a second heat exchanger to an expander, and the first        working fluid flow and the second working fluid flow exchange        heat in the suction line heat exchanger;    -   receiving a first temperature of the first working fluid flow at        a position directly upstream of the suction line heat exchanger;    -   receiving a second temperature of the first working fluid flow        at a position directly downstream of the suction line heat        exchanger;    -   determining a superheat generation based on the first        temperature and the second temperature; controlling a quantity        of flow of the second working fluid flow through the suction        line heat exchanger based on the superheat generation and a        threshold superheat value.    -   Aspect 16. The method according to aspect 15, wherein the        quantity of flow of the second working fluid flow is controlled        such that the superheat generation does not exceed the threshold        superheat value.    -   Aspect 17. The method according to aspect 16, wherein the        threshold superheat value is at or about 4° C.    -   Aspect 18. The method according to any of aspects 15-17, wherein        controlling the quantity of flow of the second working fluid        flow comprises directing a portion of the second working fluid        flow to a bypass line via a stepped three-way valve.    -   Aspect 19. The method according to any of aspects 15-17, wherein        controlling the quantity of flow of the second working fluid        flow comprises operating a plurality of controllable valves        proportionally to allocate flow between a bypass line and the        suction line heat exchanger.    -   Aspect 20. The method according to any of aspects 15-19, further        comprising receiving a third temperature, wherein the third        temperature is a temperature of the second working fluid flow,        and wherein controlling the quantity of flow of the second        working fluid flow is further based on the third temperature.    -   Aspect 21. The method according to any of aspects 15-20, wherein        the suction line heat exchanger is a counter-flow heat exchanger        wherein the first working fluid flow travels through the suction        line heat exchanger in a first direction, and the second working        fluid flow travels through the suction line heat exchanger in a        second direction, wherein the second direction is opposite the        first direction.    -   Aspect 22. The method according to any of aspects 15-21, wherein        the HVACR circuit is a heat pump circuit, the first heat        exchanger is a heat exchanger receiving working fluid from the        expander, and the second heat exchanger is a heat exchanger        receiving working fluid from a discharge of the compressor.

The examples disclosed in this application are to be considered in allrespects as illustrative and not limitative. The scope of the inventionis indicated by the appended claims rather than by the foregoingdescription; and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

1-22. (canceled)
 23. A heating, ventilation, air conditioning, andrefrigeration (HVACR) circuit, comprising: a compressor having a suctionand a discharge; a first heat exchanger; an expander; a second heatexchanger; a suction line heat exchanger, configured to exchange heatbetween a first working fluid flow, wherein the first working fluid flowis a flow of working fluid from one of the first heat exchanger and thesecond heat exchanger to the suction of the compressor, and a secondworking fluid flow, wherein the second working fluid flow is a flow ofworking fluid from the other of the first heat exchanger and the secondheat exchanger towards the expander; a flow director located upstream ofthe suction line heat exchanger with respect to the second working fluidflow, the flow director configured to provide a variable quantity of thesecond working fluid flow to the suction line heat exchanger.
 24. TheHVACR circuit of claim 23, wherein the first heat exchanger is anoutdoor heat exchanger receiving working fluid from the discharge of thecompressor, the second heat exchanger is an evaporator, the firstworking fluid flow is from the second heat exchanger to the suction ofthe compressor, and the second working fluid flow is from the first heatexchanger to the expander.
 25. The HVACR circuit of claim 23, furthercomprising a flow reverser configured to direct the working fluid from adischarge of the compressor to one of the first heat exchanger and thesecond heat exchanger.
 26. The HVACR circuit of claim 25, wherein theHVACR circuit is in a cooling mode when the flow reverser directs theworking fluid from a discharge of the compressor to the first heatexchanger, and a heating mode when the flow reverser directs the workingfluid from the discharge of the compressor to the second heat exchanger.27. The HVACR circuit of claim 26, wherein when in the cooling mode, thefirst working fluid flow is from the second heat exchanger to thesuction of the compressor, and the second working fluid flow is from thefirst heat exchanger to the expander.
 28. The HVACR circuit of claim 27,wherein when in the heating mode, the first working fluid flow is fromthe first heat exchanger to the suction of the compressor, and thesecond working fluid flow is from the second heat exchanger to theexpander.
 29. The HVACR circuit of claim 23, wherein the suction lineheat exchanger is a counter-flow heat exchanger.
 30. The HVACR circuitof claim 23, wherein the flow director comprises a stepped three-wayvalve and a bypass line.
 31. The HVACR circuit of claim 23, wherein theflow director comprises a plurality of controllable valves.